Influence of the Radial Temperature Gradient on Cladding Dilatation

In the steep radial temperature gradient existing in the cladding wall of a reactor fuel pin, migration of vacancies up and lattice atoms down the temperature gradient can take place. The transport mechanisms are thermal diffusion and diffusion due to a radial activity gradient of vacancies caused by the temperature-dependent supersaturation of vacancies. An estimation shows that thermal diffusion could contribute to cladding dilatation under fast-neutron irradiation. The enhancement of diffusion under irradiation is derived from in-pile diffusion data of copper and gold in aluminum, because corresponding data of stainless steel are not available.